Polarographic behaviour of some s-triazine herbicides and their determination by adsorptive stripping voltammetry at the hanging mercury drop electrode

Simultaneous voltammetric determination of four triazine herbicides in water samples with the aid of chemometrics

A novel differential pulse voltammetry (DPV) method was developed for the simultaneous analysis of herbicides in water. A mixture of four herbicides, atrazine, simazine, propazine and terbuthylazine was analyzed simultaneously and the complex, overlapping DPV voltammograms were resolved by several chemometrics methods such as partial least squares (PLS), principal component regression (PCR) and principal component-artificial networks (PC-ANN). The complex profiles of the voltammograms collected from a synthetic set of samples were best resolved with the use of the PC-ANN method, and the best predictions of the concentrations of the analytes were obtained with the PC-ANN model (%RPET = 6.1 and average %Recovery = 99.0). The new method was also used for analysis of real samples, and the obtained results were compared well with those from the GC-MS technique. Such conclusions suggest that the novel method is a viable alternative to the other commonly used methods such as GC, HPLC and GC-MS.

Fabrication of an electrochemical sensor based on computationally designed molecularly imprinted polymers for determination of cyanazine in food samples

A computational approach was used for screening functional monomers and polymerization solvent in the rational design of molecularly imprinted polymers (MIPs). It was based on the comparison of the binding energy of the complexes between the template and functional monomers. On the basis of computational results, acrylamide (AAM) and toluene were selected as functional monomer and polymerization solvent, respectively. The MIP, embedded in the carbon paste electrode, functioned as a selective recognition element and pre-concentrator agent for cyanazine determination by using cathodic stripping voltammetric method. The MIP-CP electrode showed very high recognition ability in comparison with NIP-CPE. Some parameters affecting the sensor response were optimized, and then the calibration curve was plotted. A dynamic linear range of 5.0-1000 nM was obtained. The detection limit of the sensor was calculated as 3.2 nM. This sensor was successfully used for cyanazine determination in food samples.

Potentiometric sensor for atrazine based on a molecular imprinted membrane

A molecular imprinted polymer (MIP) membrane for atrazine, not containing macropores, was synthesized and implemented in a potentiometric sensor. It is expected to work like a solid ISE (where the specific carrier are the imprinted sites) the specific carrier being the imprinted site. The active ion is the protonated atrazine, positively charged. To form this species the determination is carried out in acidic solution at pH lower than 1.8, in which atrazine is prevalently monoprotonated. At these conditions the membrane potential increases with atrazine concentration over a wide concentration range (3 x 10(-5) to 1 x 10(-3)M). The slope of the function E versus logc is about 25 mV/decade, showing that the atrazine form sorbed on MIP is the biprotonated one. The detection limit is determined by the relatively high concentration of atrazine released by the membrane in the sample solution at the considered conditions. It seems to be independent of the atrazine concentration in the internal solution of the sensor, but it depends on the acidity of the solution. The response time is less than 10s and the sensor can be used for more than 2 months without any divergence.

Determination of ametryn in soils via microwave-assisted solvent extraction coupled to anodic stripping voltammetry with a gold ultramicroelectrode

An extraction-anodic adsorptive stripping voltammetric procedure using microwave-assisted solvent extraction and a gold ultramicroelectrode was developed for determining the pesticide ametryn in soil samples. The method is based on the use of acetonitrile as extraction solvent and on controlled adsorptive accumulation of the herbicide at the potential of 0.50 V (vs. Ag/AgCl) in the presence of Britton-Robinson buffer (pH 3.3). Soil sample extracts were analysed directly after drying and redissolution with the supporting electrolyte but without other pre-treatment. The limit of detection obtained for a 10 s collection time was 0.021 microg g(-1). Recovery experiments for the global procedure, at the 0.500 microg g(-1) level, gave satisfactory mean and standard deviation results which were comparable to those obtained by HPLC with UV detection.

Degradation of terbutylazine (2-chloro-4-ethylamino-6-terbutylamino-1,3,5-triazine), deisopropyl atrazine (2-amino-4-chloro-6-ethylamino-1,3,5-triazine), and chlorinated dimethoxy triazine (2-chloro-4,6-dimethoxy-1,3,5-triazine) by zero valent iron and electrochemical reduction

To help elucidate the mechanism of dechlorination of chlorinated triazines via metallic iron, terbutylazine (TBA: 2-chloro-4-ethylamino-6-terbutylamino-1,3,5-triazine), deisopropyl atrazine (DIA: 2-amino-4-chloro-6-ethylamino-1,3,5-triazine), and chlorinated dimethoxy triazine (CDMT: 2-chloro-4,6-dimethoxy-1,3,5-triazine) were degraded via zero valent iron under controlled pH conditions. The lower the solution pH the faster the degradation, with surface area normalized pseudo first order rate constants ranging from 2 (+/- 1)x10(-3) min(-1) m(-2) l for TBA at pH 2.0 to 4 (+/- 2)x10(-5) min(-1) m(-2) l for CDMT at pH 4.0. Hydrogenolysis (dechlorinated) products were observed for TBA and CDMT. Electrochemical reduction on mercury showed similar behavior for all of the triazines studied; the initial product of CDMT bulk electrolysis was the dechlorinated compound. The iron results are consistent with a mechanism involving the addition of surface hydrogen to the surface associated triazine.

Ultraviolet Absorption Spectra and Dissociation Constants of Diamino-1,3,5-triazines

This paper presents ultraviolet absorption spectra of two diamino-1,3,5-triazines, namely 1,3,5-triazine-2,4-diamine (DT) and 6-chloro-1,3,5-triazine-2,4-diamine (ClDT). The spectra were fitted to the log-normal distribution. In the more energetic zone of the spectrum both compounds presented common bands, placed around 204-205 and 223-226 nm (depending on the pH of the medium). At higher wavelengths the spectra were different, with bands appearing in the range 235-267 nm. From variations of the maximum absorbances of the individual bands, the pKb values 3.5 ± 0.2 and 1.2 ± 0.1 were obtained for protonation of the ring nitrogen placed between the amine radicals of DT and ClDT, respectively, and 9.35 ± 0.2 and 11.5 ± 0.1 for dissociation of the amino groups of DT and ClDT, respectively.

Reductive deactivation of some s-triazine herbicides: Prometryne, desmetryne and terbutryne

The electrochemical behaviour (DC and DPpolarography) of the methylthio-bis(alkylamino) s-triazine herbicides prometryne, desmetryne and terbutryne on mercury electrodes has been studied in the acidity range 2.25MH2SO4 to pH 6.5. Two two-electron irreversible reduction processes were found, complicated with adsorption. At pH values higher than the protonation pKof the triazine ring (ca. 4), this protonation reaction preceded the reduction processes. Reduction mechanisms are proposed for pH < pK and pH > pK. The products obtained in the electroreduction of dilute solutions of the above herbicides show a lower toxicological effect than that of the original compounds (lower aromatic character and cleavage of the ?SCH3 group). Thus electrochemical deactivation at pH ??3.5 and at potentials around ?1.10 V (vs. the Ag/AgCl/KClsat electrode) can be a valid method to deactivate these molecules. Finally, the reductive route can be an alternative environmental degradative process in waters under strong reductive conditions, with pH values equal or lower than 3.5 pH-units, and rich in carbonaceous materials on clays. In these ambients oxidative photolytic detoxification of herbicides cannot occur.